Meanwhile, a Monmouth University Poll of likely Iowa Republican caucus-goers shows Carson with a 14 point lead over Trump. Carson leads with 32 percent, compared to Trump’s 18 percent in the poll. (The poll has a margin of error of 4.9 percent.)

Trump has derided Carson as “low-energy,” and, after the polls showed him behind, questioned the former doctor’s religion.

“I’m Presbyterian,” Trump said at a rally in Florida. “Boy, that’s down the middle of the road, folks, in all fairness. I mean, Seventh Day Adventist — I don’t know about. I just don’t know about.”

Appearing on Fox News Sunday, Carson said he didn’t want to get into a fight with Trump. “You know, I really refuse to really get into the mud pit,” he said.

But Carson said he was surprised to see Trump bring up his faith. “It’s kind of interesting because the conflict that we had a couple of months ago…he thought I was questioning his faith and he went ballistic on that,” he said. “So, it seems a little interesting that he would now be doing that.”